This invention relates to a golf ball having dimples uniformly distributed on its spherical surface and exhibiting improved and stabilized flying performance.
Golf balls having dimples distributed on its spherical surface are well known in the art. The pattern of dimple distribution on a golf ball is generally based on dimples which are circular in plane view as seen from the typical patterns shown in FIGS. 18 and 19. The design policy taken in distributing circular dimples on a spherical surface is that they are distributed as uniformly as possible, that is, the distance between adjoining dimples is as equal as possible over the entire spherical surface. This is because it is commonly believed desirable that the entire spherical surface is aerodynamically uniform. A number of proposals have been made on the basis of this concept.
Dimpled golf balls are usually prepared using a pair of mold halves which can be vertically or laterally separated. Then, an annular land where no dimples are present, known as a parting line, is formed on a golf ball at a location corresponding to the mating edges of the mold halves to be separated.
The distribution and dimensions of dimples on a spherical surface are generally designed by starting with a regular polyhedron including regular tetrahedron to regular eicosahedron, and determining the position and configuration of dimples on each surface of the polyhedron, that is, on a plane, and then projecting the determined planar dimple on a spherical surface inscribing or circumscribing the regular polyhedron. Then dimples of certain dimensions are properly distributed on a spherical surface.
A determination of the position and configuration of dimples on each surface of a regular polyhedron will be described by taking as an example a regular octahedron as shown in the perspective view of FIG. 20a. The regular octahedron is constituted by eight (8) regular triangles as shown in FIG. 20b. Determination is made by first taking a regular triangle defining one surface of the hedron as a unit, determining the position and configuration of dimples such that planar dimples are fully uniformly distributed over the entire area of the triangle, and applying the determined position and configuration of dimples to the remaining surfaces. This eicosahedron as shown in FIG. 21a is a basic structure. In this case, the position and configuration of dimples are determined with respect to a regular triangle as shown in FIG. 21b.
A determination of the position and configuration of dimples on a unit regular triangle may be carried out typically by dividing the unit regular triangle into six congruent triangles, taking as a standard unit one triangle, for example, the shaded triangle in FIG. 20b or 21b, arranging a group of planar dimples thereon, and forming the same group of planar dimples on the remaining congruent triangles.
In order that a parting line be formed which is extended along a great circle extending on the spherical surface, the unit regular triangle, and hence the standard unit, must be provided with at least one strip-like land which contributes to formation of the parting line, in other words, at least one linear portion that does not intersect the planar dimples. For this reason, strip-like lands as typically shown by thick solid lines in FIGS. 20c, 20d, and 20e must be provided when the regular polyhedron is a regular octahedron, or strip-like lands as typically shown by thick solid lines in FIGS. 21c, 21d, and 21e must be provided when the regular polyhedron is a regular eicosahedron. As shown in the figures, only those dimples having a circular plane shape are distributed within the standard unit where they do not intersect the strip-like lands.
When a regular hexahedron or cube is chosen as a basic structure, the location of a strip-like land and hence, the location of dimples with respect to the standard unit is the same as in the case of a regular octahedron because the hexahedron is in dual; relation to the octahedron. When a regular dodecahedron is chosen as a basic structure, the same procedure as in a regular eicosahedron applies.
As described above, the prior art design requires that only circular dimples are distributed within a standard unit. If the dimples are enlarged to dimensions of about 2 to 5 mm in diameter (3.14 mm.sup.2 to 19.6 mm.sup.2) capable of substantial contribution to an improvement in aerodynamic properties, then a relatively large spacial area is left between mutually adjoining circular dimples within the standard unit. Then when all such circular dimples are projected on the spherical surface, it is difficult to distribute all the dimples uniformly over the spherical surface. The resulting ball does not exhibit a fully improved or perpetually stabilized flying performance. The problem becomes particularly serious where one standard unit contains more than one strip-like land that cannot be located to intersect circular dimples.
In the area within the standard unit where no strip-like land is present, the degree of freedom of changing the location and dimensions of circular dimples is relatively high so that the dimples can be located in a relatively high density. In the area where strip-like lands are present, however, the prohibition that circular dimples should not intersect the lands reduces the degree of freedom of changing the location and dimensions of circular dimples. It is also difficult to locate circular dimples of the diameter capable of exerting their own function in proximity to the strip-like land, and thus a land of a relatively large area remains in such a region. Particularly in the presence of more than one strip-like land within a standard unit, when every standard unit is projected on a spherical surface, a land of a large area is formed at the opposite sides of each land on the spherical surface corresponding to the strip-like land as well as about the intersection of lands on the spherical surface.